Fig. 4: In situ spectromicroscopic analysis of the organo-mineral coating on biochar surfaces and pores.
From: Microspectroscopic visualization of how biochar lifts the soil organic carbon ceiling
a A pore in biochar that was recovered from the Historical plots (scanning electron microscopy [SEM]). Bar, 50 μm. b Surface of the organo-mineral layer inside the biochar pore from Historical plots (SEM). Bar, 200 nm. c Organo-mineral clusters on a biochar surface from the Control+Recent plots (high-angle annular dark-field scanning transmission electron microscopy [HAADF-STEM]); d the electron energy loss spectra (EELS) at positions 1–5 of the clusters in (c). e A deposit attached to the surface of biochar from the Historical plots (HAADF). f 2D elemental mapping of the boxed area in e (energy-dispersive spectroscopy [EDS]. g EELS of the boxed area in (e). h Mapping integration of EELS regions 1–3 in (g). i Average soft X-ray (SXR) emission spectra of field-extracted Control+Recent (1-y) and Historical (9.5-y) biochars (n = 9, CV < 3%). j Dissolved organic content (DOC) of Historical+Recent and Control+Recent soils (liquid chromatography-organic carbon detection [LC-OCD]). The hydrophilic fraction is further sub-divided into five categories: biopolymers, persistent C, building blocks, low molecular weight acids, and low molecular weight neutral molecules.
